1. Field of the Invention
This invention relates to a magnetic recording medium and to a method for the manufacture thereof. More particularly, this invention relates to a magnetic recording medium such as for video tape, audio tape and magnetic disc which is improved by the inclusion of abrasive in the magnetic layer thereof or to a method for a manufacture thereof. More specifically, this invention relates to a magnetic recording medium having various properties enhanced by improving dispersibility of abrasive in the magnetic layer and to a method for the manufacture thereof.
2. Description of Prior Art
Heretofore it has been customary to produce the magnetic recording medium such as a magnetic tape by the steps of thoroughly mixing acicular-shaped or granular magnetic metal particles, additives such as abrasive, and a binder in a ball mill, applying the resultant mixture on a substrate film such as polyester film, and drying the composite film thereby forming a magnetic layer on the substrate film.
In recent years, the recording density of the magnetic recording medium has steadily increased. This trend has necessitated development of a magnetic recording medium having improved S/N ratio and enhanced surface property. Various suggestions have been made with a view to fulfilling the requirement. One of them resorts to addition of a dispersant for improving the dispersibility of magnetic powder and other additives in the binder. Conventionally, however, the addition of the dispersant has been effected by simply adding the dispersant to a mixture of magnetic powder, additives and binder and stirring the resultant mixture. If the dispersant is added by this method, however, the improvement of dispersibility sought by the addition of the dispersant is not fully attained because of the difficulty of dispersion of solid particles in the mixture. Thus, this method has attained the improvement in the S/N ratio, for example, only to a nominal extent.
An object of this invention, therefore, is to provide an improved magnetic recording medium and a method for the manufacture thereof.
Another object of this invention is to provide a magnetic recording medium having various properties enhanced by the improvement of dispersibility of abrasive in the magnetic layer thereof and a method for the manufacture thereof.